Neuronal accumulation of various mutant or damaged proteins results in several neurodegenerative disorders, including Parkinson's disease, ALS, and polyglutamine expansion disorders. Toxic abnormal species can aggregate in cells, and there is an ongoing discussion of how protein aggregation influences neurotoxicity. It has recently become clear that in contrast to protein aggregation in a test tube, aggregation of damaged or mutant polypeptides in vivo is a complicated and tightly regulated process that involves many cellular factors. Using a yeast model of polyglutamine (polyQ) expansion disorders, the PI has carried out a number of genetic screens and found that mutations in several components of the machinery that organizes cortical actin patches (CP) dramatically reduce polyQ aggregation. Furthermore, elimination of CP by arp2 or arp3 mutations completely blocks aggregation of polyQ in cells. This proposal will test the hypothesis that cortical actin patches play a direct role in polyQ aggregation. Accordingly, investigations will be carried out to determine if polyQ-containing polypeptides aggregate at CP sites, and the role of Rnq1 prion in these interactions. The role of components of CP and factors responsible for formation of actin cables in polyQ aggregation will be evaluated. An important goal would be to establish whether CP play a general role in protein aggregation, including aggregation of distinct proteins important for neurological disorders, e.g. synphilin 1, alpha-synuclein and PABP2, and in formation of yeast prions. A critical question will be whether homologs of major components of CP play similar role in polyQ aggregation in mammalian cells. A special focus will be to evaluate a hypothesis that interactions between CP and polyQ are mediated by certain SH3-domain proteins, e.g. Sla1, Rvs167, Bem1 or Hof1. Previous work from the PI's lab showed that polyQ aggregation causes early defect in endocytosis in yeast and mammalian cells. In a separate aim we will test a hypothesis that polyQ aggregation causes inhibition of endocytosis in neurons, using a C. elegans model. It will also be established whether mutations that increase the lifespan and delay the onset of polyQ aggregation in worms also delay the onset of endocytosis defects. Exploration of fundamental mechanisms of protein aggregation that we undertake in this project will help to understand the nature of several neurological disorders.